Dr. Priscila Kienteca Lange, NASA Post-Doctoral Fellow and Scientist (Universities Space Research Association), Ocean Ecology Laboratory, NASA’s Goddard Space Flight Center, Greenbelt, MD
Research interests: Using satellite ocean color data to study how different types of phytoplankton influence marine life and biogeochemical cycles, and how they respond to physical and chemical processes.
Research highlights: When it comes to making life on Earth possible, microscopic phytoplankton are the big dogs on the block. These minute creatures are responsible for approximately half of Earth’s primary production, not to mention at least half of Earth’s oxygen. Since phytoplankton are the base of virtually all marine food webs, the presence and health of phytoplankton are essential to ocean productivity.
While it is possible to study phytoplankton simply by dipping a net or bottle into the water and using a microscope to examine the collected critters, sensors aboard Earth observing satellites make it possible to study these organisms across huge distances using data collected over many years. Satellite-collected data combined with data collected by scientists aboard research vessels plying the world’s seas are the foundation of Dr. Priscila Kienteca Lange’s research into phytoplankton biomass and distribution.
The term “phytoplankton” refers to a diverse group of single-celled aquatic organisms that contain chlorophyll and produce energy through the process of photosynthesis. They can further be broken down into two types: single-celled algae known as protists, which includes the common diatoms that are found near coasts; and primitive photosynthetic bacteria (cyanobacteria), some of which are really, really tiny (about a micron across in size, which is 0.000039 of an inch). But don’t let their size fool you—as Lange notes, cyanobacteria are the most abundant photosynthetic organisms in the sea.
Much of the satellite-collected data used by Lange come from NASA’s Ocean Biology Processing Group (OBPG) located at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. These data are archived at and distributed through NASA’s Ocean Biology Distributed Active Archive Center (OB.DAAC), which is responsible for ocean biology data in NASA’s Earth Observing System Data and Information System (EOSDIS) collection.
While sensors orbiting hundreds of miles above Earth can’t “see” microscopic organisms, they can detect differences in water reflectance caused by their presence. Phytoplankton contain pigments, like chlorophyll, that absorb the energy from light that is used in the photosynthetic process. Different types of phytoplankton have unique combinations of pigments that change the reflectance of the water when they are present. Satellite-borne sensors can detect this reflectance as well as changes in this reflectance over time.
One specific measurement used by Lange is remote sensing reflectance, which is notated Rrs. Rrs is a powerful tool for quantifying the amount of phytoplankton chlorophyll in the surface ocean and in distinguishing key phytoplankton types. After calibration with shipboard-collected measurements, Rrs-based satellite observations of phytoplankton enable the assessment of large-scale ecosystem changes based on the distribution and amount of different phytoplankton types, and aid in the development and improvement of models used to estimate phytoplankton biomass.
The Rrs data product used by Lange is available through NASA’s OB.DAAC, and is produced from data collected by the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument aboard NASA’s Aqua Earth observing satellite. Launched in May 2002 with six instruments to study Earth’s water cycle, five of Aqua’s instruments (including MODIS) are still collecting valuable data, including data related to phytoplankton and dissolved organic matter in the oceans.
Along with Aqua MODIS Rrs data, other Aqua MODIS data products used by Lange (and available through NASA’s OB.DAAC) include Sea Surface Temperature (SST), Photosynthetically Active Radiation (PAR, which measures the amount of light available for photosynthesis), chlorophyll concentration, and diffuse attenuation coefficient (which is abbreviated Kd and is a measurement of how the penetration of light dissipates with depth in a column of water).
For the past few years, Lange has concentrated her phytoplankton research in the largest ocean ecosystems: subtropical gyres. A gyre is a system of ocean currents that rotates clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere. Five principal gyres extend across roughly 50 percent of Earth’s ocean area: the North and South Pacific Subtropical Gyres, the Indian Ocean Subtropical Gyre, and the North and South Atlantic Subtropical Gyres (the Gulf Stream current along the U.S. East Coast forms the western boundary of the North Atlantic Gyre).
The nutrient-poor waters of these gyres are dominated by the smallest and most abundant photosynthetic organism on Earth: Prochlorococcus. The pigments within this cyanobacterium can change the color—and thereby the reflectance—of water, making it possible to study this organism across large distances using remotely-sensed data.
Previous studies have shown that the overall warming of the world’s oceans is leading to an expansion of subtropical gyres. A recent study by Lange and her colleagues shows that this warming also is leading to changes in the distribution of Prochlorococcus. Using both ship-collected data and satellite-collected measurements, the research team found that distribution of Prochlorococcus within the gyres is expanding vertically, which is leading to a tremendous shift in phytoplankton biomass. Along with warming temperatures of the water column within the gyres, the vertical distribution of Prochlorococcus also is closely linked to available light, so the biomass of phytoplankton under the ocean surface can be estimated based on satellite-collected measurements of how far light can penetrate into the water column.
As Lange and her colleagues observe, the warming of ocean surface layers within subtropical gyres enables Prochlorococcus to survive at greater depths. This, in turn, leads to a shift in phytoplankton biomass to lower levels of water within these gyres. As phytoplankton biomass moves to lower levels in the water column, this, in turn, removes phytoplankton biomass from upper levels of the water column and allows greater amounts of solar radiation to penetrate more deeply into the water column. Through this feedback loop, the gyres’ waters continue to warm and phytoplankton continue to move to lower levels where the sunlight now penetrates. The research team notes that a decrease in the abundance of Prochlorococcus at the surface is compensated by an increase of Prochlorococcus at depth. Thus, while Prochlorococcus biomass is decreasing at the surface, the overall biomass of this organism is actually increasing throughout the entire water column since it now exists at lower levels.
The distribution of phytoplankton, whether in subtropical gyres or in the highly productive waters of the Arctic and Antarctic, will continue to adjust to take advantage of changing ecological conditions. This shift in biomass that forms the base of the aquatic food pyramid will have significant impacts for the survival of animals that feed on the surface and those the feed farther below the surface. Instruments aboard Earth observing satellites are providing the data needed by Lange and her colleagues in their studies looking at how microscopic phytoplankton continue to be the big dogs on the block when it comes to facilitating life on Earth.
Representative data products used:
- Aqua/MODIS data products; available through NASA's OB.DAAC:
- Sea surface temperature (SST; doi:10.5067/AQUA/MODIS/L3M/SST/2014)
- Remote sensing reflectance (Rrs; doi:10.5067/AQUA/MODIS/L3M/RRS/2018)
- Photosynthetically active radiation (PAR; doi:10.5067/AQUA/MODIS/L3M/PAR/2018)
- Chlorophyll concentration (CHL; doi:10.5067/AQUA/MODIS/L3M/CHL/2018)
- Diffuse attenuation coefficient (Kd; doi:10.5067/AQUA/MODIS/L3M/KD/2018)
- Various data products from the OB.DAAC SeaWiFS Bio-optical Archive and Storage System (SeaBASS) data repository: https://seabass.gsfc.nasa.gov; SeaBASS is a publicly shared archive of in situ oceanographic and atmospheric data maintained by NASA’s OBPG
- Various data products from the British Oceanographic Data Centre (BODC) data repository; available at https://www.bodc.ac.uk/data/
Read about the research:
Lange P.K., Brewin, R.J.W., Dall’Olmo, G., Tarran, G.A., Sathyendranath, S., Zubkov, M.V. & Bouman, H.A. (2018). Scratching beneath the surface: a model to predict the vertical distribution of Prochlorococcus using remote sensing. Remote Sensing, 10(6): 847. doi:10.3390/rs10060847
Brewin, R.J.W., Tilstone, G.H., Jackson, T., Cain, T., Miller, P.I., Lange, P.K., Misra, A. & Airs, R.L. (2017). Modelling size-fractionated primary production in the Atlantic Ocean from remote sensing. Progress in Oceanography, 158: 130-149. doi:10.1016/j.pocean.2017.02.002
Lange, P.K., Tenenbaum, D.R., Tavano, V.M., Paranhos, R. & Campos, L.S. (2014). Shifts in microphytoplankton species and cell size at Admiralty Bay, Antarctica. Antarctic Science, 27(3): 225-239. doi:10.1017/S0954102014000571